174. INVESTIGATION OF A STRATIFIED BAROTROPIC MIXING LAYER WITH COORDINATE SYSTEM ROTATION

Abstract
Submesoscale ocean dynamics are characterized by stable stratification and significant, but far from dominant rotational effects. We focus our study on a barotropic mixing layer having Rossby and Froude numbers initially of O(1). Both linear stability analysis (LSA) and direct numerical simulations (DNS) are performed to analyze the model problem. LSA results suggest that strong stratification (Fr < 1) tends to stabilize the inertial instability, while increasing the range of vertical wavenumbers associated with barotropic instability. A new LSA result is that, when absolute vorticity is nearly zero at the inflection point, the range of vertical wavenumbers associated with barotropic instability greatly increases. Correspondingly, DNS of the nonlinear evolution show significant destabilization of an anticyclonic mixing layer including a rapid increase of the vortex stretching term when the flow transitions through the zero absolute vorticity state. A network of coherent longitudinal vortices emerges in the anticyclonic cases, while coherent vorticity evolves very similarly between the non-rotating and cyclonic cases. In the anticyclonic cases, breakdown into small-scale turbulence and secondary instabilities in localized regions of intensified vertical shear are also observed.